The invention lies in the semiconductor technology field. More specifically, the present invention relates to a method of reading electrical fuses/antifuses (fuses are electrical breakdown paths or fusible links) in a semiconductor memory configuration, in which the state of a fuse/antifuse is read by applying a voltage to the fuse/antifuse. In the semiconductor memory configuration the high potential of bit lines of a memory cell array is defined by a voltage Vblh which is reduced with respect to an internal voltage Vint of the semiconductor memory configuration.
In integrated circuits, such as in particular in semiconductor memory configurations, electrically burnable fuses/antifuses are being used to an increasing extent. These are capable in each case either of being switched on (antifuse) or switched off (fuse) by burning. A fuse that can be switched off by burning is severed by the burning operation and is also referred to as a normal xe2x80x9cEfusexe2x80x9d. On the other hand, a fuse that can be switched on by burning is switched on by the burning operation and is referred to as an xe2x80x9cantifusexe2x80x9d. Such an antifuse is also rendered conductive by the burning. In the following text, xe2x80x9cfusexe2x80x9d is to be understood to mean both an xe2x80x9cEfusexe2x80x9d and an xe2x80x9cantifusexe2x80x9d (given appropriate reversal of the result of the burning operation).
Referring now to FIGS. 2 and 3, there is shown a fuse configuration 1 having different fuses 2 which are located between terminals 3, 4. If, then, such fuses, xe2x80x9cEfusesxe2x80x9d in the present case, are burned, then the electrical connection between the terminals 3 and 4 is interrupted, as indicated schematically for two of the fuses 2 in FIG. 3. This burning can be carried out by applying appropriately high electrical voltages between respective terminals 3, 4 or as a result of the action of a laser beam.
At present, fuses are mainly read with the aid of the so-called internal chip voltage Vint, which is available in the chip of each semiconductor memory configuration and is about 2 V, or with the aid of the external supply voltage Vdd. FIG. 4 shows a circuit configuration suitable for this purpose, with which the individual terminals 3 of the fuse configuration 1 can be supplied with the internal chip voltage Vint via switches. If a fuse is nonconductive, that is to say burned, then this can be assessed as a logic state xe2x80x9c1xe2x80x9d (or xe2x80x9c0xe2x80x9d). If, on the other hand, a fuse is conductive, that is to say not burned, this is then determined as a xe2x80x9c0xe2x80x9d state (or xe2x80x9c1xe2x80x9d.
We have now for the first time discovered that reading fuses by means of the internal chip voltage Vint, which is of the order of magnitude of 2 V, can lead to problems: this is because the application of such a high voltage has the effect of a relatively rapid aging process and in this way can ultimately even bring about inadvertent burning of previously unburned fuses.
The object of the present invention is to provide a method of reading electrical fuses and/or antifuses which overcomes the It above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and in which rapid aging processes and inadvertent burning of previously unburned fuses/antifuses are reliably avoided.
With the above and other objects in view there is provided, in accordance with the invention, a method of reading electrical fuses/antifuses in a semiconductor memory configuration, which comprises:
providing a semiconductor memory configuration with fuses/antifuses and with a memory cell array having bit lines, the semiconductor memory having a given internal voltage and a high potential of the bit lines defined by a reduced voltage having a level below the given internal voltage; and
reading a state of a fuse/antifuse by applying the reduced voltage defining the high potential of the bit lines of the memory cell array.
In other words, the object of the invention is achieved in that the fuses/antifuses are read by applying the reduced voltage Vblh.
The terms fuses/antifuses and fuse/antifuse are to be understood as inclusive alternatives. The novel method is thus defined for reading fuses and/or antifuses and for semiconductor memory devices which are provided exclusively with fuses or antifuses.
In accordance with an added feature of the invention, the reduced voltage is reduced by approximately 20 to 30% with respect to the internal voltage.
In accordance with a concomitant feature of the invention, the internal voltage is set to about 2 V and the reduced voltage is set to about 1.6 V.
In semiconductor memory configurations, such as DRAMs, the high potential of the bit lines, as is known, is defined by the voltage Vblh. This voltage Vblh is about 1.6 V and is therefore reduced by 20 to 30% with respect to the internal chip voltage Vint. If, then, instead of the previously conventional internal chip voltage Vint, the reduced voltage Vblh that defines the high potential of the bit lines is used to read the fuses/antifuses, then because of the voltage reduction from about 2 V to about 1.6 V that is effected as a result, the average lifetime of the fuses (Efuses and antifuses) can be increased by about 1.6 decades, that is to say by a factor 16, as trials by the inventors have shown.
This considerable increase in the lifetime as a result of a relatively slight reduction in the read voltage of the fuses/antifuses is completely surprising and could not be foreseen; this is because the relatively slight reduction in the reading voltage by 20 to 30% allows an increase in the lifetime by 1.6 decades, that is to say 1600%, to be achieved. With reference to this increase in the lifetime, the invention has proven to be even more advantageous for antifuses than for Efuses.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of reading electrical fuses/antifuses, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.